This invention relates generally to video recording and reproducing systems, and, more particularly, to such systems utilizing compression techniques for increasing the effective amount of video information that can be stored on, or retrieved from, a recording disc.
Various systems are available for recording signals at video frequencies on discs, tapes and other media, utilizing optical, magnetic, and other techniques. In particular, some disc recording systems utilize a radiant energy beam to effect an irreversible change to the disc surface, and thereby write information on the surface for later reproduction. Information can be recorded on a disc in the form of a continuous spiral track, in which case a recording transducer is continually translated in a radial direction as the disc is rotated. It is also possible to record video or non-video information in concentric circular recording tracks on a disc.
In order for video disc players to be competitive with video tape machines, the video discs employed should be capable of storing reasonable lengths of program material. Without some form of compression of the video information, the total amount of information that can be stored on a given disc is limited by the diameter of the disc, the width of the recorded track, and the lineal data density that can be written and reproduced by the system.
In accordance with a prior invention of the present inventor, now the subject of U.S. Pat. No. 3,908,080, entitled "Method of Making an Extended Play Video Disc Record", video information can be recorded in a compressed form on a disc. In this prior technique, instead of recording all of the video information only one out of a predetermined number of successive sequential video frames is recorded. For example, a compression ratio of two-to-one is obtained if alternate frames can be recorded, and the data storage requirement is then reduced by fifty percent. On playback, each recorded frame is reproduced twice, and provision is made to preserve the audio information corresponding to all of the original frames of video information.
Although the system described and claimed in the aforementioned patent represented a substantial advance in the field of the invention, there are many situations in which such a technique is not wholly satisfactory. When the video image changes very rapidly, it would be more satisfactory to record and reproduce every frame of the program in sequence. Similarly, there may be other occasions when there is practically no change in picture content over several consecutive frames, in which case a compression ratio of even greater than two-to-one would be desirable. Consequently, there has existed, until the present invention, a need for a more versatile video compression system than the one described in the aforementioned patent. The present invention satisfies this need.